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Physical Properties and Observables of the Warm/Hot IGM

Physical Properties and Observables of the Warm/Hot IGM. Frits Paerels Columbia University a nd SRON Utrecht. The Warm and Hot Universe, Columbia, May 7, 2008. Approximate Physical Properties of the WHIM Deviations from Equilibrium Which WHIM? The effect of Galactic Winds

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Physical Properties and Observables of the Warm/Hot IGM

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  1. Physical Properties and Observables of theWarm/Hot IGM Frits Paerels Columbia University and SRON Utrecht The Warm and Hot Universe, Columbia, May 7, 2008

  2. Approximate Physical Properties of the WHIM Deviations from Equilibrium Which WHIM? The effect of Galactic Winds X-ray Spectroscopy and Absolute Measurements

  3. 1. The WHIM: approximate physical properties Gravitational collapse: shocks heat the diffuse IGM ½ mp(lH0)2 = 3/2 kT; l = 1 Mpc: T = 2 x 105 (l/1 Mpc)2h702 K Detailed DM/Hydro simulations: - overdensitiesδ ~ few, to few dozen; but with large range in density; - physical density d <nB> = d2 x 10-7 cm-3 (!!) - average T correlates with δ, but with large spread, 105-7 K - metallicity: ??, from Z/ZO = 0.01 (Lyα forest) to 0.3 (clusters); probably strongly density-dependent May hold up to ~40% of the baryons at z=0

  4. WHIM highly ionized; at z=0, shocks + X-ray photoionization ionize O up to He- and H-like unique spectroscopic signature in X-ray transitions

  5. Detection? Nicastro et al. 2005 Mkn 421 Chandra LETGS Wavelength (Å) Rasmussen et al. 2007 Scharf et al., 2000 (ROSAT) δ ~ 100 XMM RGS (see also Luca Zappacosta, Alexis Finoguenov, and Jan Willem den Herder)

  6. 2. Deviations from Equilibrium Physical density very low: many processes out of equilibrium, even over Hubble time (e-i equilibration, heavy ion ionization equilibrium, importance of photoionization, radiative cooling, thermal stability; interesting effects on shock structure? (B!); particle acceleration, effect of nonthermale- on ionization balance and line excitation, ….) All of these have effects on spectroscopy of heavy ions!

  7. Which WHIM? The effect of Galactic Winds Without winds With winds Cen & Ostriker, 2006

  8. X-ray Spectroscopy and Absolute Measurements Emission line intensity + absorption line EW: n2L, nLn, L (for assumed abundance, ionization balance) Of special interest: the He-like n=1-2 ‘triplet’; O VII: 21.6, 21.8, 22.1 Å Intercombination Resonance Forbidden R, I, F line ratio’s sensitive to excitation mech (CX, rec.), Te, ionization non-eq., … Capella, Chandra HETGS (Canizares et al. 2000)

  9. Absolute Abundances Churazov et al. (2001): I(forbidden, intercombination): CX, recombination  A n2L I(resonance): CX, recombination  A n2LPLUS resonance scattering of CXB continuumAnL If sources of the CX resolved out: WHIM filaments light up in resonance line! Emission spectroscopy of O VII triplet equivalent to absorption/emission; At δ = 30, Te = 106 K: scattered/thermal resonance line emission ≈ 2 ! With reasonable assumption for L, get A. Definite advantage of imaging emission line spectroscopy: contrast; 3D; estimate absolute densities, abundances Requirements in terms of spectroscopic resolution: modest (ΔE ~ 2 eV)

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